Tire Size Comparison Calculator with transparent formulas, clear units, and instant results. Diameter change: Ø = R × 25.4 + 2 × W × A ÷ 100; Δ% = (Ø₂−Ø₁) ÷ Ø₁ × 100.
Stable formula
This calculator uses a stable mathematical formula. Always verify the values you enter.
Accuracy level
High when inputs and units are correct.
Last reviewed
July 9, 2026
Formula or source
Stable mathematical formula explained on the page.
Guide reading time
4 min
Confidence
High for the stated calculation.
Result type
Formula result, not an official certification.
Do not use for: Cases with missing data, unclear units, or a required professional certification.
How Tire Size Comparison Calculator works
The Tire Size Comparison Calculator uses these inputs: Original tire width (mm), Original aspect ratio (%), Original rim diameter (in), New tire width (mm), New aspect ratio (%). Its primary output is Diameter change. The calculation uses the entered tire and wheel geometry.
The engine implements Ø = R × 25.4 + 2 × W × A ÷ 100; Δ% = (Ø₂−Ø₁) ÷ Ø₁ × 100. Validation runs first to reject zero divisors and non-finite values.
Numeric example using the starting values: Tire Size Comparison Calculator: Original tire width (mm): 205 · Original aspect ratio (%): 55 · Original rim diameter (in): 16 · New tire width (mm): 205. The resulting output is Diameter change: 0.00%.
Tire Size Comparison Calculator: This result is a calculation estimate only. It does not approve installation, safety, legality, or vehicle fitment. Verify it with the vehicle manufacturer, a qualified professional, and local law. Suspension, fender, brake, load, speed-rating, and legal clearance cannot be approved from geometry alone.
💡 Useful Tips
Do not mix units between Original tire width (mm) and Original aspect ratio (%); make sure both describe the same scenario. Verify fitment against manufacturer specifications, approved sizes, and a qualified installer.
Do not treat Tire Size Comparison Calculator — Diameter change as mechanical, safety, legal, or financial approval.
Frequently Asked Questions
What does Diameter change mean?
It is the direct output of the formula and entered values, and applies only to the defined scenario.
Which inputs change the result?
The active inputs are Original tire width (mm), Original aspect ratio (%), Original rim diameter (in), New tire width (mm), New aspect ratio (%). Changing any one runs the same formula again. A small diameter difference does not guarantee mechanical or legal fitment.
What to check next
The result is a starting point. For a clearer picture, continue to a related calculator or read a short guide that explains the assumptions.